Glass feeders

ABSTRACT

A basin for a forehearth of a glass-making furnace having an internal volume divided into upper and lower portions by an annular shoulder is described wherein the horizontal cross-sectional area of the upper portion is significantly greater than that of the lower portion. The base of the basin has a glass discharge outlet therein. In use, the discharge outlet is aligned with a relatively movable cylinder which acts as a flow metering valve. The cylinder can be rotated about its axis at a constant or adjustable speed, or the cylinder can be non-rotating and have a separately driven stirrer movable about it to prevent or reduce the formation of stagnant areas.

This is a continuation of application Ser. No. 08/146,200, filed asPCT/GB92/00895, May 18, 1992 published as WO92/20630, Nov. 26, 1992, nowabandoned.

FIELD OF INVENTION

This invention relates to glass feeders and, in particular, to feederarrangements for feeding molten glass from a furnace forehearth to oneor more processing stations where the molten glass is converted intouseful objects, for example, bottles and jars.

BACKGROUND OF THE INVENTION

In the production of glass objects, particularly the mass production ofbottles and jars, on a continuous basis, it is of considerableimportance to be able to control the characteristics of the glass as itleaves the furnace and moves towards an appropriate forming unit, forexample an independent section container forming machine of known type.

It is well appreciated that major problems can arise in terms ofconsistency of manufacture if great care is not taken to operate underhomogeneous and effectively invariant conditions. The problem, however,is that the attainment of such conditions is particularly difficult toachieve.

Conventionally, glass is manufactured by charging the raw materials intoone end of an essentially elongate furnace while applying heat, forexample from oil burners, to heat the raw materials and fuse themtogether to form a glassy mass. The glassy mass moves away from theingredient feed point, down the furnace, gradually becoming more andmore homogeneous. It then flows, very slowly since it is very viscous,into a number of channels, perhaps as many as six or eight in a largefurnace, known as forehearths and at the end of each channel there islocated in the floor of the channel an aperture through which moltenglass is discharged.

By ensuring a sufficient length of forehearth, and by applyingappropriate insulation and/or heating, it is possible to ensure that, bythe time the glass reaches the end of the forehearth and is ready fordischarge, it is relatively free of bubbles and has a relatively stableinternal pattern of temperature and viscosity. It is not, however, easyto ensure that discharge from the forehearth is always even.

A major problem arises from the fact that the glass, when discharged,must be in a highly viscous state, so that it may be moulded and, at thesame time, cooled such that as it is moulded to its final shape, it hascooled to a temperature at which it is effectively sufficiently rigid tomaintain that shape during subsequent cooling and annealing steps.Because the glass on discharge to the forehearth is highly viscous, andbecause, in any event, it moves very slowly, attempts to control theprecise temperature and homogeneity of the emergent glass are fraughtwith difficulty.

In order to be able to control the overall flow of glass from theforehearth, it is a known practice to provide located above the apertureor apertures in the forehearth through which molten glass may pass, ametering cylinder which may be lowered on to the forehearth floor toprevent glass flow, and may be raised to permit glass to flow under itsedge and through the aperture or apertures in the forehearth floor. Inoperation, such a cylinder may be rotated about its axis when it hasbeen raised a little way from the forehearth floor, and such rotationcan assist in homogenising the glass, but only to a limited extent.Alternatively, the cylinder may be stationary, and other stirringmembers moved in the glass to promote an homogeneous glass conditionwithin the region above the aperture(s). Actual discharge of the moltenglass through the aperture is conventionally achieved by the use of oneor more vertically reciprocating plungers above the aperture(s) whichact to form successive gobs of glass below the aperture which are cutoff by synchronised shears to fall into a chute and be transported to aforming station.

Such a system is disclosed, for example, in U.S. Pat. No. 3,133,803,and, in addition, in that case flow may be adjusted by the use of avertically-adjustable skimmer block set in the roof of the forehearthand which acts as a gate under which molten glass flows before runningacross a shallow land and down an inclined wall set to one side of awell into which the glass then flows and which surrounds the meteringcylinder and gob plunger, and in which a shallow layer of molten glassforms. The glass is spread out in an attempt to render it more easilyheatable or coolable, but such spreading out leads to problems of unevenflow and possible bubble entrainment.

Such an approach using a thin glass layer is unconventional, and has notbeen adopted widely in practice. In contrast, conventionally, the depthof glass in a forehearth is 100 to 160 mm, this depth being a compromisebetween making the forehearth sufficiently shallow that the temperatureof the glass passing through it can be quickly controlled with littlethermal lag, and making the forehearth deep enough to enable sufficientglass to flow along it. The discharge end of the forehearth isconventionally even deeper, for example 200 to 350 mm, giving areservoir of glass of supposedly even characteristics from which gobsare successively drawn.

BRIEF DESCRIPTION OF INVENTION

We have now found surprisingly that substantially improved homogeneity,together with improved possibilities for glass condition control, may beachieved by relating the shape of the discharge end of the forehearth tothe provision of a glass-flow metering cylinder.

Thus, according to a first feature of the present invention, there isprovided a dispenser basin for the forehearth of a glass-making furnaceand intended to be full of glass when in use, the basin having in itsbase a glass-discharge outlet, and having in its internal surface asubstantially-annular shoulder notionally dividing the basin volumevertically into a lower portion and an upper portion, in which the lowerportion has a horizontal cross-sectional area which is substantiallyless than that of the upper portion, and in which the depth of theshoulder from the intended free surface of the glass in the basin isabout half the depth of glass in the basin during use, and a sleeve inthe upper portion of the basin, characterised in that the sleeveconstitutes a metering cylinder which projects downwardly into the lowerportion of the basin, and is movable vertically whereby the gap ofadjustable width between the bottom of the sleeve and the base of thebasin functions as a metering orifice.

The metering cylinder may be rotated as well as being movablevertically.

In the use of such a basin, it is found that the consistency of theoutput of molten glass from the orifices in the floor of the basin,whether that output be a continuous flow or in the form of successivegobs, is substantially improved with respect to conventional knownarrangements. The exact reasons for this are not clear, but it appearsthat treatments designed to assist in conditioning the glass andrendering it homogeneous in the forehearth continue to operate on thelarger surface area upper region of molten glass, while in the lower,relatively much smaller cross sectional area, section, a rapid,homogenised effectively helical flow of glass downwardly is achievedwithout difficulty. The flow is helical if the tube is rotated.

Because of the relatively small volume of the lower section (and thecorrespondingly short passage time therein for the molten glass) it isbelieved that inhomogeneities do not have a chance to build up and theresulting outflow shows a high degree of consistency leading to easieroperation and, in particular, fewer reject items.

The present invention may be applied to feeding units both forcontinuous feed of molten glass and intermittent feed. It is ofparticular value in glass feeder arrangements where, within the rotatingcylinder, are located one or more axially reciprocable gob plungerswhich cooperate with one or more corresponding apertures in the base ofthe forehearth to generate a train of successive gobs of molten glasswhich are passed to successive stations in a glass container formingmachine or the like.

The detailed construction of the pouring basin in accordance with thepresent invention may vary very widely and will vary with the particularinstallation, type of glass, desired feed rate and the like. However, itis possible to make some general observations relating to theconstruction.

First of all, the basin may be of monolithic construction or made up byassembling a number of refractory shapes together. Monolithicconstructions are preferred and according to a specific feature of thepresent invention, there is provided a glass-pouring basin having anopen top and an apertured base, the top having a lateral inlet forconnection to a forehearth, and the internal volume of the basin beingnotionally divided into an upper larger horizontal cross-sectional areasection of substantially the same depth as the forehearth channel and,divided therefrom by a region of the inner wall of the basin, having invertical section a convex shape, a lower substantially-smallerhorizontal cross-sectional area section, the vertical depth of the lowersection being substantially equal to that of the upper section. Theshape of the wall of the basin in section may vary from three distinctlines, two vertical and one horizontal, with a squarish shoulder or kneedividing the upper from the lower section of the basin, to a smoothercurve including an inflexion between an upper concave section startingnear the top of the basin and a lower convex section terminating at thefloor of the basin. Preferably, the horizontal cross-sectional area ofthe lower portion of the basin is essentially constant.

By substantial equality in connection with the vertical depths of glassin the two sections is not meant a mathematical equality but rather ageneral approximate equality, though this can itself vary withinrelatively wide limits. Indeed, it may not be particularly clear exactlywhere the lower section merges into the upper, particularly if the wallhas not got a clearly defined annular shoulder but, for example, asloping shoulder. Generally speaking, the transition from the upper tothe lower region will occur at 40 to 60 percent of the total glass depthin the basin in use.

If desired, associated with the upper part of the basin (though they mayalso be provided for the lower smaller horizontal cross sectional areasection) there may be glass condition sensors, for example temperatureor viscosity sensors, and/or means to temper or condition the glass, forexample heating means or particular insulation means.

BRIEF DESCRIPTION OF DRAWINGS

The invention is illustrated by way of example with reference to theaccompanying drawings in which:

FIG. 1 is a typical diagrammatic section through the end of a forehearthin accordance with known feeder design;

FIG. 2 is a view corresponding to FIG. 1 but showing the end of theforehearth provided with a basin in accordance with the presentinvention;

FIGS. 3 and 4 are respectively known and inventive structures, againillustrated diagrammatically, for a feeder designed to have a higherthroughput of molten glass than those shown in FIGS. 1 and 2respectively.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings, like reference numerals are used throughoutto denote like parts. Thus common to all four structures is a refractorylined forehearth 1 through which molten glass flows in the direction ofthe arrow 2 towards a feeder. At its end, the feeder is constructed as arefractory lined or monolithic basin 3 having in its base 9 aglass-discharge outlet 7 closed in turn by a closure member 8 having init one or more apertures 4 through which glass may stream, or gobs ofglass may be pressed by means of a vertically reciprocating pair of gobplungers 5 actuated by means not illustrated in the drawing. For thesake of clarity, the top structure, which is conventionally locatedabove the feeder and which may, for example incorporate heating means,has been omitted.

Surrounding the plungers is a refractory hollow metering cylinder 6which is slowly rotated and which may be raised and lowered to leave agap between its lower end and the floor of basin 3 when it is desired todispense and adjust the flow of glass through the outlet apertures.

The known structure of FIG. 1 does not lead to particularly homogeneousoutput from the apertures. However, when, in accordance with the presentinvention, the basin is divided into an upper portion 10 and a lowersmaller cross-sectional area portion 11, it is surprisingly found thatimproved results are obtained. Preliminary experiments with structuresin accordance with the invention have shown that the molten glass tendsto flow gently and homogeneously through the forehearth channel into thetop portion of the basin maintaining good homogeneity and is thenrapidly and symmetrically moved down in the annular space between thecylinder 6 and the outer walls of the lower portion of the basin asmolten glass is drawn through the apertures. With the gob feederarrangement shown, the glass has only a relatively short dwell time inthe lower space between the basin wall and the rotating cylinder, so itstays homogeneous while it is formed into gobs and ejected through theapertures 4.

A particular advantage or the basin design in accordance with thepresent invention is that it may be operated in simple fashion to avoidthe formation of large and essentially stagnant volumes of molten glass.These tend to form in the upper regions of known pouring basins, andlumps of relatively more viscous glass can tend to break off from thestagnant regions and become entrained in, but not homogeneously mixedwith, the glass as it flows out of the basin, thus leading toinhomogeneities in the products made from the glass. We have found thatsuch problems may be minimised or alleviated entirely when operatingwith a basin in accordance with the present invention by regularlyvarying the rotational speed of the refractory cylinder and hence movingthe location of the stagnant region. The effect is enhanced if the upperportion 6a of the refractory cylinder which is located in the uppersection of the basin is of larger diameter than the lower portion 6bthereof located in the lower section of the basin.

Further advantages of the basin structure of the present inventionconsist in the availability of a relatively larger upper surface areafor temperature control of the body of glass in the basin compared tothe volume of the basin itself as contrasted with known basin designs.The narrower lower region, however, lends itself to fine temperaturecontrol, for example achieved by the provision of extra insulation orextra heating, thus improving the overall controllability of the glassdispensing process at the output end of the forehearth.

The basic design according to the present invention provides theadvantages outlined above when used in connection with fixedcylinder/separate stirrer arrangements as well as with the rotatingcylinder arrangement illustrated.

The detailed geometry and geometrical ratios may be varied widelywithout departing from the scope of the present invention. In contrastto the prior art basins, which were not divided into upper and lowerregions, clearly distinct from one another, the present invention, byproviding that division, provides a considerably improved homogeneity ofglass output together with enhanced control possibilities.

It is within the purview of the present invention for the basin to bemade and sold as a separate product. This permits it to be retro-fittedon to the forehearth of an existing furnace. The manner in which thebasin could be connected to a forehearth does not form part of thesubject-matter of this invention, and so will not be described herein inany greater detail.

I claim:
 1. A dispensing basin for molten glass at the discharge end ofa forehearth of a glass-making furnace wherein the dispensing basin hasa base and side walls; said basin has a lower portion of horizontalcross-sectional area which is substantially less than a horizontalcross-sectional area of an upper portion thereof; said basin includes atleast one discharge outlet in said base, at least one reciprocatableplunger which extends into the upper portion and the lower portion ofthe dispensing basin and which cooperates respectively with said atleast one discharge outlet to form successive gobs of molten glass ateach of said at least one discharge outlet, and a rotatable sleevemember present in the upper portion and lower portion of said basin andsurrounding respectively each of said at least one reciprocatableplunger; said basin includes a first horizontal annular shouldersurrounding said at least one discharge outlet; and wherein spacingbetween said sleeve member and said first horizontal annular shoulderserves to meter the flow of molten glass; the improvement comprisingproviding a second annular shoulder in said basin above said firstannular shoulder, said second annular shoulder being located such thatsaid second annular shoulder is substantially at half the depth ofmolten glass which is present in the basin during use of the basin fordispensing molten glass, whereby to provide surrounding a lower portionof the sleeve member, an annular space through which molten glass flowsfrom said upper portion of the basin to said spacing between said sleevemember and said first horizontal annular shoulder.
 2. A basin accordingto claim 1 wherein side walls forming the lower portion of said basinare substantially concentric with said at least one discharge outlet. 3.A basin according to claim 2 wherein the horizontal cross-sectional areaof the lower portion of said basin is essentially constant.
 4. A basinaccording to either claim 1, 2 or 3 wherein said at least one dischargeoutlet has a first end through which molten glass enters and a secondend through which molten glass exits, and is closed at the second end bya closure member having at least one aperture therein which is smallerin cross-sectional area than that of said at least one discharge outlet.5. A basin according to claim 1 further comprising a means for rotatingsaid rotatable sleeve member at an adjustable speed.
 6. A basinaccording to claim 1 or 5 wherein said rotatable sleeve member includesan upper portion of a first diameter and a lower portion of a seconddiameter wherein the second diameter is smaller than said firstdiameter, and said lower portion of said rotatable sleeve member iscircumscribed by the lower portion of said basin when said rotatablesleeve member is in operation.